Thinning Can Reduce Losses in Carbon Use Efficiency and Carbon Stocks in Managed Forests Under Warmer Climate

Forest carbon use efficiency (CUE, the ratio of net to gross primary productivity) represents thefraction of photosynthesis that is not used for plant respiration. Although important, it is often neglected inclimate change impact analyses. Here we assess the potential impact of thinning on projected carbon cycledynamics and implications for forest CUE and its components (i.e., gross and net primary productivity andplant respiration), as well as on forest biomass production. Using a detailed process-based forest ecosystemmodel forced by climate outputs of five Earth System Models under four representative climate scenarios, weinvestigate the sensitivity of the projected future changes in the autotrophic carbon budget of threerepresentative European forests. We focus on changes in CUE and carbon stocks as a result of warming, risingatmospheric CO2 concentration, and forest thinning. Results show that autotrophic carbon sequestrationdecreases with forest development, and the decrease is faster with warming and in unthinned forests. Thissuggests that the combined impacts of climate change and changing CO2 concentrations lead the forests togrow faster, mature earlier, and also die younger. In addition, we show that under future climate conditions,forest thinning could mitigate the decrease in CUE, increase carbon allocation into more recalcitrant woodypools, and reduce physiological-climate-induced mortality risks. Altogether, our results show that thinningcan improve the efficacy of forest-based mitigation strategies and should be carefully considered within aportfolio of mitigation options.